As is known, turbine blades are rotating airfoil-shaped components designed to convert thermal energy from a working fluid such as gas or steam into mechanical work via the turning of a rotor. There is generally a minimum physical clearance requirement between the tip of the turbine blade and an outer casing for safety and other concerns. This clearance, however, also allows the escape of the some of the working fluid without performing useful work. Performance of a turbine thus may be enhanced by sealing the outer edge of the turbine blade to prevent the working fluid from escaping into the gap. A tip shroud may be used on the blade to seal such a gap. Tip shrouds may enhance turbine performance and also may serve as a vibration damper. A tip seal also may be used on the shroud to minimize leakage into the gap.
The use of a tip shroud, however, may add weight to the overall turbine blade. The heavier the turbine blade, the more centrifugal force created during blade rotation and, hence, the more load and stress placed on the turbine blade and other components. Moreover, the tip shroud also may curl due to a bending load on the edges of the shroud from gas pressure as well as the centrifugal force. Although curl may be limited by providing a thicker tip shroud, the increased thickness generally involves adding even more weight to the tip shroud. Other types of turbo machinery face similar issues.
There is thus a desire for a tip clearance control systems and methods with an improved tip shroud design. Such improved systems and methods for limiting leakage preferably should limit the leakage flows through the tip gap so as to increase overall turbine efficiency but without the additional weight that may impact and limit component lifetime.